Screw-propeller.



No. 700,36 5. Patented May 20, I902 c. A; PARSONS. sqmaw PBOPELLER.

Applicatioxg filed Dec. 22, 1900. mo Moduli) 2 Sheet-Sheet I.

I200 Ca. fizz/aroma.

a w 4wawy - Patented May 20, 1902; C. A. PARSONS. f

SCREW PBUPELLER.

(Applicafiion filed Dec 22, 1900.)

2 Sheets-Sheet 2.

(No Model.)

YHE mums PETERS co vnotcumon WASHINGTON, u. c.

' CHARLES ALe Rno masons, OF nEwoA sTtE-UPonTYNE,ENGLA D, I l

a of Northumberland, England,have invented 1 behind the blades; l

reduce such cavitation;

.others it has been established that the normal pressure on aplane moved at small in-' approximately as the square of the distance great cavitation first commences near thetips which attends high-speed propellers arises proximately asitheangleof inclination and SCREW-PR OPELLERQ SPECIFICATION forming part of Letters Patent No. 700,365 dated May 20, 1902. I Application filed December 22, 1900. Serial No. 40,774. (No model.)

To all whom itmtty concern:

Be it known that L-CHARLES ALGERNON PARSONS, engineer, asubject of the King of Great Britain and-Ireland, residing at Heaton Works, Newcastle-upon-Tyne, in the county certain new'and useful Improveme'nts'in and Relating to Screw-Propellers, (for which I have made application =forLette-rsPatent in Great Britain,;No. 9,792, bearing date May 28, 1900;) and I-do herebydeclare that the folof the same. r ,7 v e My invention relates to screw-- propellers for fast ships, especially to those for use where ity. I find by experiment that the cavitation principally in two placesenamely, at the back faces of the blades near the tips and 1 around the conical tip of the propeller-boss The object of my invention is to remove or According to the experiments of'Dines'and clinations through: air or water varies apthe square of the velocity ofmotion. Now in a screw-propeller ofthe usual pitch ratio say from one to fifteenpitch' coefficient-the angle of inclination of the blade to the direction of motionthrough the water is approximately the same for'sueh distances from the shaft-line as lie outside about-two-fifths of the radius of the propeller-circle, while the velocity of these points through the water varies approximately as the. distance from the shaft. From this it followsthat the pressure upon the water of any element of the blades (between the above limits)..wi1l vary of the element from the shaft-line. In highspeed vessels when the water-pressures are of the blades (as .I have; proved experimentally) and extends toward the roots of the blades as the speed or slipratio of the propeller is increased.

the water'tends to close in around the after cone, following the principle in hydrodynam icsflthat the angular momentum in a vort x tends to remain constant. I Theanghlar veloc- The cavitation which is found to-take place propeller is dueto the rotational velocit'yim-* I parted to the water in thevicinity'of the boss by their skin-andeddyfriction onthe water, which rotational velocity increases'rapidly 'as ity of the water around thecone is therefore much in excess faces ofzthe propeller-blades near the tips by,

their tips."- e

The second part of myinventionconsists of propellers in ordinary use."

To obtain ahigh mean slip ratio'andjthrus't, I without .producing serious. cavitation has Y been the object ofmany-inventors;' but'.their 3 j 80 made,'among.otherth ings, in the' direction of J 5' f" increasing-the pitch of the blades toward 1: their points. 'I"haveascertainedlthatthe I desiredeffect .is produced by forming fastrunning propellers with'a reducing pitch to wardtheir tips, the-reduction commencingab'outjone-half totwo-thirds outward frornf 1 the boss or blade root, suchreduotion ofpitch Y j i 1 increasing to about a ten-per-c'ent. reduction i efforts to effectthistend have hitherto been atthe blade-tips. Theoretically'also it would appear, first, that this variation oflpitch' should be such that theslip ratio at any given distance from the shaft-' should-be'ininverse v proportion to the squareof :that distance; v I

second, that cavitation wofuld commence Sir 'in providing small vaneson'thepropeller 1 'coneadap'tedto prevent cavitation "around the cone and to-utilize Tor-propulsion some; I of the rotational energy of the watercloseto the propeller-cone, which is lost with the type,

. inultaneously over a large area of propeller- I blade thus constructed"; third, that such pro-i pellers could be run faster without producing cavitation, while at the same time efiecting a greater mean slip ratio and thrust than too of that of the'prop eller-cone itselfQ. I y l forming the blades 'wi.th]a reducedpitch near' would be possible with propellers constructed with blades of constant or increasing pitch toward their points. I have confirmed this by OXPGIlIIIOHtS OH propellers constructed according to my invention which isv based on this theory.

In order to clearly explain the difference between an ordinary propeller and one constructed according to my invention, 1 have appended two sheets of drawings, in which- Figures 1 and 2 are elevation and plan, respectively, of an ordinary propeller, the latter view showing blade-sections a, b, c, d, e, andfon the linesA A, B B, O C, D D, E E, and F F, respectively, of Fig. 1. A diagram of the pitch variation of this propeller is also shown in Fig. 2. Figs. 3 and 4 are elevation and plan, respectively, of my new construction of propeller with reduced pitch, the plan showing blade-sectionsg, 7t,j, 7a, m, and H on the lines G G, H H, J J, K K, MM, and N N, respectively, of Fig. 3. A diagram of the pitch variation of my propeller is also shown in Fig. 4 for comparison with that shown in Fig. 2. Figs. 5 and 6 are elevation and plan of a propeller provided with vanes. Fig. 7 is a section through A A of Fig. 5, drawn to an enlarged scale.

The first partof myinvention is illustrated by Figs. 1 to t, inclusive.

In the propellers illustrated in Figs. 1 and 2 the angle of inclination of the blade from section 0 c outward to the tip of the blade is approximately constant, while the pitch of the blade increases continuously from c 0 out to the tip, but is constant from c c inward to the root-section ff. A diagram representing the pitch variation of the propeller seen in Fig. 2 may be obtainedin this manner: Along the horizontal axis of the propeller from its intersection with the vertical blade-axis set off a distancep equal to one-fourth of the pitch of the blade at the root-section f f and erect here a perpendicular line. Set off along this perpendicular line a distance? equal to the radius of the root-section ff. Now since the pitch of the blade does not vary at the three sections e e, cl d, and c c distances P, P, and 1", corresponding respectively to the radii of these sections, may be set off along this perpendicular line. The pitch of the blade increases, however, from section a o outward. Set off, therefore, distances q and 7 to represent one-fourth of the pitch of the section b b and a ct, respectively. Erect perpendiculars Q and R their lengths corresponding, respectively, to the radii of sections (9 b and a (t. Then a curve drawn through the points 1, 2, 3, 4, 5, and 6 will represent the pitch Variations of the propeller-blade, while a line from each point drawn to the intersection of the horizontal and vertical axes of the propeller gives the major axis, and consequently the inclination of each blade-section. It will be observed that sections a (L and b b have the same inclination to the direction of motion as each other and that the inclination of section a c varies very little from them.

Referring now to the propeller constructed according to my invention and illustrated in Figs. 3 and 4-, the pitch of the blade is constant from the root-section 02 7t outward to a point about midway between the sections 7c 7: andjj; but it decreases from this point outward to the tip of the blade. The line of pitch variation 1 or this propeller may be obtained in the same manner as in the case just described. Let the distance in from the vertical axis of the blade represent one-fourth of the pitch of the three sections 71 71,011. an, and 7c and distances u, t, and .9 represent one-fourth of the pitch at sectionsjj, h h, and g g, respectively. By erecting perpendicular lines from the horizontal axis at these distances and setting off lengths thereon corresponding to the radii of the various sections points 7, 8, 9, 10, 11, and 12 are obtained, and the line passing through them represents the pitch variation of my propeller. Asis also the case in Fig. 2, a line drawn from these points to the intersection of the horizontal and vertical axes of the propeller gives the inclination of the various blade-sections to the direction of motion. I have found that propellers constructed as just described with reference to Figs. 3 and 4c can be run at a higher speed without the production of cavitation and with a higher mean slip ratio and thrust than has hitherto been possible.

In carrying the second part of my invention into effect as illustrated by Figs. 5, 6, and '7, I provide small vanes v c on the cone as of the propeller-shaft 1 which vanes may be parallel to the shaft, as shown, or set at a moderate angle thereto, with a pitch of the same or opposite hand to the propeller itself. In my experiments I have found that when three vanes are provided on the cone and set parallel to the shaft, as illustrated, with their outer edges practically parallel to the center line of the shaft the cavitation produced around the cone as at a given speed is largely reduced or entirely prevented. .As hereinbefore explained, the angular velocity of the water around the cone is much in excess of that of the propeller-cone itself; but vanes such as those just described retard the water vortex around the cone with two beneficial results-first, some of the angular mo mentum of the water vortex that would otherwise be lost is imparted to the vanes, and consequently assists in rotating the shaft, and, secondly, owing to the diminution of the angular velocity of the water around the shaft the water more easily closes in and presses on the cone abaft the propeller-boss, thus imparting an additional forward thrust to the shaft.

What I claim as-my invention, and desire to the propeller-conebehind the blades, snb to secure by Letters Patent, is stantiallly as described; Y .7 1. A screw-propeller provided with blades In witness whereof I-havehereunt0 set my Constructed with a, reduced pitch-toward their hand in presence of two witnesses.

5 tips, the'reduction commencing from about 7 CHARLES "ALGERNON PARSONS.. 'one-halftotwo-thirdsoutward fromthe blade- Witnesses: t r roots, substantially as described. WILLIAM HENRY PILMOUR, v

Ascrew-propellerharing vanes seen-red WILLIAM DAGGETT. i 

